1. Field of the Invention
This invention relates to cryogenic refrigeration systems; and more particularly, to a modular architecture for helium compressors within such cryogenic refrigeration systems.
2. Description of the Related Art
In conventional systems, about 10% of heat generated by a helium compressor is transferred into the helium, but this helium should be cooled to less than 20° C. for best performance, both for Gifford McMahon (GM) type cryocooler systems and pulse tube cryocooler based systems. The majority of the heat load in such systems is attributed to cooling the oil, but the oil does not need to be cooled below around 50° C. as long as the flow rate stays high, for example about 3.0 gallons per minute. Thus, there are distinct cooling requirements for each of the helium and the oil used in the cryogenic refrigeration system. This distinction has not been appreciated in traditional water-cooled or air-cooled helium compressors.
FIG. 1 shows a heat exchanger 10 having chilled water flowing therethrough, wherein cold chill water flows into an inlet in the heat exchanger 10, and circulates within an interior volume of the heat exchanger 10, before exiting as warm chill water out of an outlet of the heat exchanger 10. Hot helium is introduced through a first conduit 20 within the heat exchanger, and is cooled to yield cool helium flowing out of the first conduit 20. Similarly, hot oil is introduced through a second conduit 30 within the heat exchanger, and is cooled to yield cool oil flowing out of the second conduit 30. The hot helium and hot oil are each introduced at an end of the heat exchanger where the chill water is exiting, in theory to provide a maximum cooling gradient therebetween. Notice that each of the oil and the helium are collectively cooled by the heat exchanger, effectively cooling both the oil and the helium to some extent, but not very efficiently. Here, the oil consumes most of the cooling power of the heat exchanger, and the helium is not cooled sufficiently to yield maximum performance of the cryogenic refrigeration system.
For example, U.S. Ser. No. 12/832,438, filed Jul. 8, 2010, titled “AIR COOLED HELIUM COMPRESSOR”, describes a conventional system that is embodied with a combination Helium and Oil heat exchanger unit; the contents of which are hereby incorporated by reference. Although the '438 application claims novelty of the placement of an oil cooler outdoors (as opposed to indoors) for maintaining a cool indoor environment, the embodiments described therein lend evidence of the state of the art where independent cooling requirements of the helium and oil within the system are not addressed independently, but rather, collectively.
The embodiments as described and claimed herein present an improvement over conventional architectures for helium gas compressors within such cryogenic refrigeration systems.